Researchers are testing out a new tool for GPs, to help them ask patients those difficult questions about their weight.

A University of Otago study has found some GPs struggle discussing obesity with an overweight patient because they're afraid of offending them.

The researchers are currently trialling a simple prompt tool, to help in obesity conversations.

There has been a steady increase in New Zealand's obese population in the past 30-years and Lead researcher Lesley Gray says GPs need help.

"There's a prompt on the screen in much the same way as you would have a prompt for taking your blood pressure or maybe a screening."

She says weight is a very personal thing and some doctors don't want to ruin patient relationships by raising it.

"The practitioner knows that weight may be a risk factor for some health conditions and generally speaking the patient is well aware of their size shape and weight and yet both parties dance around the issue."

Gray says the Health Ministry will assess how well the tool is working before deciding whether to roll it out across the country.